1. Field of the Invention
This invention relates to a paper ejection apparatus equipped on the latter stage of an image formation apparatus in a print apparatus.
2. Background Art
FIGS. 4 and 5 show the configuration of a paper ejection unit in a related art.
A paper ejection unit 2 has a paper transport roller 4 for transporting paper 1 sent from an image formation apparatus 3 to the following stage, a paper stack table 6 (simply, stack table) being supported movably up and down for stacking and storing paper 1 transported from the paper transport roller 4, a slidable paper alignment member 7 being placed in parallel with the stack section paper transport direction for pressing both end parts of the paper 1, thereby aligning the paper 1, a slidable paper alignment member 8 being placed in an orthogonal direction to the stack section paper transport direction for pressing the tip of the paper 1, thereby aligning the paper 1, a rotation member 9 for pressing the rear end part of the paper 1 on the stack table 6 in a vertical direction, a comb-teeth-like paper rear end stopper 15 being fixed upright at a constant position in the proximity of the rotation member 9, a plurality of paper top face press rollers 5 placed to press the top face of the paper 1 ejected onto the stack table 6, and detection means 10 for detecting the top face of the paper stack face. Hitherto, a configuration wherein the paper 1 is stacked on the stack table 6 for storage while the stack table 6 is moved down with an increase in the stack amount of paper ejected onto the stack table 6 has been known.
This kind of paper ejection unit may be connected to the latter stage of an image formation apparatus such as a laser beam printer for use. The recent image formation apparatus enables the operator to select a double-sided print mode for recording and forming a toner image on both sides of paper, a face-up eject mode for ejecting paper with the toner image face upward, a face-down eject mode for ejecting paper with the toner image face downward, etc., as the operator desires.
As the image formation apparatus, an electrophotographic apparatus using an electrophotographic process is known. As a technique of fixing a toner image formed on paper on the paper, generally a thermal fixing roller technique is adopted in the image formation apparatus (electrophotographic apparatus). As for paper ejected through this kind of thermal fixing roller technique, the both-end edge parts of the paper parallel with the paper transport direction warp to the toner image face and tend to easily curl because of thermal shrinkage, etc., by the heating action and the component fiber direction of the paper itself. Therefore, for example, if paper is ejected in the face-up eject mode after a toner image is thermally fixed on one side of the paper, the paper easily curls upward; if paper is ejected in the face-down eject mode, the paper easily curls downward.
In the paper ejection unit in the related art, a problem remains for change in the paper stack state depending on the paper curl direction caused by the paper eject mode of the image formation apparatus. Particularly, when downward curl paper ejected in the face-down eject mode is stacked, if the paper stack amount exceeds 1,000 sheets, the top face of the stacked paper section is bent like an inverse U shape as the downward paper curls are accumulated. The stack table height is controlled based on the height position of the proximity of the bend part top face detected by the paper top face detection means. On the other hand, as downward curls accumulated, the both-end edge part vicinities of paper particularly parallel with the paper transport direction may be lowered about 5 mm to 10 mm below the bent part top face.
There is a technique wherein a slidable paper alignment member being placed in parallel with the stack section paper transport direction for pressing both end parts of paper, thereby aligning the paper presses both end parts of the paper edges parallel with the paper transport direction, thereby aligning the paper while the paper alignment member repeats sliding in an orthogonal direction to the paper transport direction. However, it occurs that an overlap between the paper alignment member and the stacked paper top part becomes extremely small or vanishes. In this case, a problem of inaccurate paper alignment on the paper stack top in the paper ejection unit occurs.
Such a phenomenon appears noticeably with downward curls hard to correct by paper""s own weight.
It is therefore an object of the invention to provide a paper ejection apparatus for making it possible to reliably stack paper and provide good paper alignment on a paper stack table regardless of paper eject mode, particularly in a face-down paper eject mode.
To attain the above-mentioned object, in the invention, a projection part is provided at a position in the proximity of paper top face detection means in a paper stack direction on a paper stack table.
The projection part is positioned upstream in a paper transport direction from the center of the paper stack table and has a slope upstream in the paper transport direction.
The projection part can be attached to and detached from the paper stack table.